This invention relates generally to parking brake control devices and more particularly to parking brake control devices that have a torsion lock parking brake actuator.
U.S. Pat. No. 3,315,538 granted to Norman N. Fender Apr. 25, 1967 discloses a parking brake control device that has a torsion lock parking brake actuator. The parking brake actuator has an operator lever that is pivotally mounted on a frame and attached to a cable for actuating the parking brake. The operator lever includes a sector gear that meshes with a pinion gear. The pinion gear is part of a drum that is rotatably mounted on the frame. Rotation of the drum is controlled by a torsion lock comprising a coil spring that is wound snugly around the drum with tabs at each end. One tab is anchored to the frame and the other tab is not attached and free to move. This unattached tab lies in the travel path of a release lever that is also pivotally mounted on the frame.
The parking brakes are set by pressing down on a foot pad attached to the operator lever which rotates the sector gear. The sector gear rotates the pinion gear in a direction that releases the tight grip of the coil spring on the drum so that the sector gear and pinion gears can rotate. After the parking brakes are applied, the operator lever is released and held in the depressed position by the tight grip of the coil spring on the drum which prevents counter rotation of the meshed sector and pinion gears. The parking brakes are released by actuating the release lever, which engages the unattached tab at the free end of the coil spring and unwinds the tight grip of the coil spring on the drum. The parking brakes are then released under the action of the parking brake springs which also return the operator lever to an off position via the cable that actuates the parking brake. The release lever may be manually or power actuated.
The torsion lock parking brake actuator has the well known advantage of holding the operator lever in any position so that the parking brake can be applied with virtually any desired pressure. However, the torsion lock parking brake actuator also has the well known disadvantage of requiring a separate release mechanism which is actuated independently of the operator lever for releasing the parking brake.
There are other types of parking brake actuators that are foot operated and have the capability of releasing the brakes by pushing down on the pedal that is attached to the operator lever. See for example, U.S. Pat. No. 2,905,024; U.S. Pat. 2,915,916; U.S. Pat. No. 3,079,809 and U.S. Pat. 3,511,107.
However, these parking brake actuators do not have the advantage of the torsion lock parking brake actuator, namely, the ability to hold the operator lever in any position so that the parking brake can be applied with virtually any desired pressure.